Conventionally, in the field of lubricating base oils, attempts to improve cold flow property and a low-temperature viscosity property of a base oil contained in a lubricant (lubricating base oil) have been executed.
In a process of producing a lubricating base oil, treatment of reducing the content ratio of a normal paraffin contained in a lubricating base oil (dewaxing treatment) is generally performed so as to improve cold flow property. Thus, in a producing step of a lubricating base oil, dewaxing treatment such as solvent dewaxing and isomerization dewaxing is widely performed.
Solvent dewaxing is a treatment in which an oil to be treated (lubricating base oil before dewaxing treatment) is mixed with a solvent to be cooled and a deposit (wax component) in the mixture is removed by filtration or the like. Moreover, isomerization dewaxing is a treatment in which a wax component in an oil to be treated is reduced by, in the presence of hydrogen, bringing the oil to be treated into contact with an isomerization dewaxing catalyst to convert (isomerize) mainly a normal paraffin into an isoparaffin. Although isomerization of a normal paraffin to an isoparaffin may occur in hydrocracking that is one of hydrotreatment, while cracking of various components contained in an oil to be treated is main in hydrocracking, isomerization is main in isomerization dewaxing, and thus, both are distinguished.
Furthermore, Patent Literature 1 discloses a method for producing a lubricating base oil, in which the contents of a normal paraffin that has a harmful effect on cold flow property and a specific isoparaffin are reduced by performing hydrocracking/isomerization dewaxing such that the urea adduct value of an obtained lubricating base oil is within a predetermined range.